A. Deckert et C. Dewey, THE INFLUENCE OF OVULATION RATE, EARLY EMBRYONIC DEATH, AND UTERINE CAPACITY ON LITTER SIZE IN SWINE, The Compendium on continuing education for the practicing veterinarian, 16(9), 1994, pp. 1237
Despite extensive efforts, average litter size has improved at a very
slow pace during the past 20 years. Litter size is determined by uteri
ne capacity or ovulation rate minus early embryonic death, whichever v
alue is smaller. Selection for just one trait, therefore, does not sub
stantially increase litter size. Ovulation rate is an important compon
ent that maximizes reproduction in pigs; this rate establishes the cei
ling for litter size. Ovulation rate is associated with breed and incr
eases with parity. Among other factors, losses may be attributed to ea
rly embryonic death that occurs during the first 30 days of gestation.
Early embryonic death is affected by nutrition, season, time of breed
ing, and semen quality. Uterine capacity is the number of piglets that
the sow can carry to term. Insufficient uterine capacity leads to fet
al death after 30 days of gestation and can also result in low and var
iable birth weights.